An exoskeleton comprises, generally, a pelvis structure, two leg structures, two foot structures and two hip structures:                The pelvis structure is configured to be positioned behind the kidneys of a user when wearing the exoskeleton and may be fixed to the pelvis by means of a harness or straps.        Each leg structure is configured to be positioned facing one of the legs (left or right, depending on the structure) of the user, and comprises an upper leg segment and lower leg segment, arranged to face the thigh and the calf of the user, respectively.        Each foot structure also comprises a support plane on which one of the feet (left or right, depending on the structure) of the user may be supported when the foot lays flat.        Each hip structure is configured to be positioned facing one of the hips (left or right, depending on the structure).        
Complete control of the exoskeleton requires actuators and structural links to allow movement of the exoskeleton and thus allow displacement of the user wearing the exoskeleton. The mechanical links typically comprise pivot links, sliding links and/or ball joint links, while the actuators may comprise cylinders, motors, etc.
These mechanical links and the actuators are selected to allow the movement of the exoskeleton without hurting the user who wears it. To this end, it is especially important not to apply forces that the user's limbs cannot withstand and to offer an exoskeleton having both a low profile and a moderate weight.
WO 2011/002306 for example describes a system for controlling an exoskeleton worn by a user and having actuators associated with different members of the exoskeleton each corresponding to a body part of the user. The exoskeleton comprises in particular a main foot actuator and a secondary foot actuator, configured for actuating the foot structure and enable it to adapt to the terrain.
To this end, the main foot actuator is configured for actuating rotation of the foot structure relative to the lower leg structure using a pivot link about an axis parallel to a pivot axis of the knee. The secondary foot actuator meanwhile is intended to allow the foot structure to adapt to the terrain. However, such an ankle structure is relatively complex, bulky, heavy and energy intensive.
There has also been proposed, in document FR 14 52370, filed on Mar. 21, 2014 on behalf of the Applicant, an exoskeleton comprising a leg structure, a foot structure and an ankle pivot link connecting the foot structure to the leg structure, wherein the ankle pivot link has an oblique pivot axis, i.e. a pivot axis that does not fall within any reference plane among the front plane, the sagittal plane and the horizontal plane of the exoskeleton. Thus, the ankle pivot link forms a non-zero angle comprised between 0° and 30° with the support plane of the foot structure, and a non-zero angle comprised between 0° to 45° relative to a plane perpendicular to the median longitudinal axis of the support plane. Such a configuration having the advantage of producing movements at the ankle which are similar to natural human movements with only one actuator oriented as shown above. The structure of the exoskeleton is simplified and lightened. Furthermore, this configuration reduces the lateral use of space of the leg, thus reducing the risk of collision during a walking motion.